How the contents of a filthy gully can be a money-spinner
‘Circular economy’ approach could potentially save £4.3 million and 1,000 tonnes of carbon over four years
Move over Marmite – when it comes to turning waste matter into usable products, there’s a new contender for the champion’s crown.
The ‘love it’ or ‘hate it’ spread is made using yeast extract, a by-product of the beer brewing process and is an early example of recycling and the ‘circular economy’ – where waste products are utilised, rather than disposed of.
Now Oxfordshire County Council is applying these same principles in a completely different area – road repairs and gully cleaning. Over a four year period, the approach could potentially stop 1,000 tonnes of CO2 being emitted and save £4.3 million of council taxpayers’ money. It will also cut the amount of waste that is sent to landfill sites and reduce the amount of new material that is dug out of the ground.
It's difficult to imagine anything useful being salvaged from the dirty water and solid matter – largely silt – recovered by tankers during the process of cleaning gullies. But you’d be surprised.
Oxfordshire County Council contractor Skanska is currently taking part in a trial with the company Combined Drier Technology to reprocess and reuse the waste, thereby reducing the amount that has to be disposed of expensively.
Using purpose-built de-watering bays in the county council’s depot in Drayton, near Abingdon, water is removed and filtered. Depending on the quality, the water can be re-used or discharged into the foul drainage network under a trade effluent discharge consent.
The de-watered gully waste is then dried, allowing it to be screened and graded, recovering as much of the original waste as possible and removing any non-recyclable contaminants. These recycled materials could then potentially be used in highways works as fill material for resurfacing, topsoil replacement, or be fed into the production of recycled aggregates, subject to appropriate material and chemical testing results and stakeholder agreement. During the trial period, this drying and screening is being undertaken at a third-party permitted facility. However, the equipment used is mobile which would allow it to be deployed to the Drayton depot if the trial proves successful.
Councillor Yvonne Constance, Oxfordshire County Council’s Cabinet Member for Environment, said: “This initiative is a great example of the new thinking and commitment that will be needed to meet our climate action goals. We’re pleased to have been able to collaborate on this with Skanska and their supply chain to reduce both costs and carbon emissions with an innovative solution.”
Oxfordshire produces approximately 1,000 tonnes of gully waste annually. If successful, the new methods of dealing with it could save up to £27,000 a year and prevent four tonnes of CO2 being released into the atmosphere.
Despite only being seven months into the trial, refinements are being made all the time. These include plans for the generators – which were previously diesel powered but now use gas-to-liquid fuel – to run on hydrotreated vegetable oil, cutting emissions by 90 per cent compared to diesel.
The Drayton depot is also home to a mobile plant which processes waste generated from repairs to the county’s roads.
One of the by-products of road and path resurfacing – created as a result of asphalt being removed from a surface sub-base – is known as ‘asphalt planings’. Annual maintenance of Oxfordshire’s highway network produces significant quantities of this material, which can be recycled. However, approximately 8,000 tonnes of this are classified as ‘asphalt waste containing coal tar’ (AWCCT), a toxic material which makes it expensive to dispose of safely and difficult to recycle.
But Skanska – through the efforts of OCL Regeneration Ltd, a company within its supply chain – has found a way of treating and utilising the AWCCT and thereby reducing Oxfordshire County Council’s annual hazardous waste costs.
Asphalt planings are transported to the OCL plant at Drayton where they are crushed, graded and then mixed with foamed bitumen, cement and water to form a cold lay asphalt material, which can then be re-used elsewhere in road maintenance. This means that the scheme minimises the use of ‘virgin’ materials to reconstruct roads.
The process also involves treating the material at Skanska’s Horton-cum-Studley recycling site – specially chosen as journey distances were 60 per cent shorter than those for importing virgin materials. All the parties involved maximise carbon savings by making sure every journey between Drayton and Horton-cum-Studley involves full lorries – transporting material to be recycled one way, and the finished product in the opposite direction.
To a large extent, these changes are as much about altering mindsets as they are about amending working practices.
Waste is now being recognised as a potential feedstock for the recycling process, rather than something which needs to be disposed of as quickly and as cheaply as possible – whilst also adhering to legal requirements. And rather than following the carbon-intensive linear pattern – where new, virgin materials are sourced for projects – more thought is given to the use of recycled materials, and planning of up to a year in advance is carried out so that this can be achieved in suitable areas.
Oxfordshire County Council, along with Skanska and OCL Regeneration Ltd, recently took part in a webinar organised by the Institute of Environmental Management and Assessment to highlight its pioneering work in developing the circular economy.
All these changes, and many more, feed into Oxfordshire County Council’s ambitions to tackle climate change. Last year, the council approved its Climate Action Framework, which set out its plans to make itself a carbon neutral authority by 2030, and to enable Oxfordshire as a whole to become zero-carbon by 2050.